"Back in the 80s, the Commodore C-64 had an intelligent floppy drive, the 1541, i.e. an external unit that had its own CPU and everything. The C-64 would send commands to the drive which in turn would then execute them on its own, reading files, and such, then send the data to the C-64, all over a propriatory serial cable. The manual for the 1541 mentioned, besides the commands for reading and writing files, that one would read and write to its internal memory space. Even more exciting was that one could download 6502 code into the drive's memory and have it executed there. This got me hooked and I wanted to play with that - execute code on the drive. Of course, there was no documention on what code could be executed there, and which functions it could use." Very interesting. I'm most interested in how he describes others taking his work, and making it better. This would be impossible today, thanks to Microsoft, Apple, and other patent trolls.

More or less quite the contrary? At least some Seagate drives seem to have a real serial port, one to which you could connect with a VT100 dumb terminal (for example to wake up / "unconfuse" seemingly "failed" drive: https://sites.google.com/site/seagatefix/ )

IIRC drive controllers are quite often built around some ARM core now (counting all peripherals, I guess it's not entirely unlikely that a modern PC has, on average, more ARM cores than x86 ones?); then there are firmware updates.

Too bad in too many places the Datasette never really ceased to be a standard... (at least I sometimes had a chance to play with desktop C128 of my cousin) Still not that bad, with fast loaders for Datasette also being a standard.